This invention relates to apparatus and methods for taking teeth impressions and, more specifically, for taking registered impressions of upper and lower teeth and converting these impressions into castings which are used for analysis by the dentist, displays for patient consultations, laboratory work, and, when properly mounted and registered, for correct bite registration. Present methods for preparing these castings require taking upper and lower impressions with separate, sequentially applied trays filled with a hardening paste. Upon hardening, a separate plaster casting is made from each tray. If is often desirable to register the castings so that they fit together in the same manner as if in the patient's mouth. This has previously been accomplished by placing a relatively thin sheet of wax between the teeth and having the patient bite into the wax to form a simultaneous impression of both the upper and lower teeth as they fit together. This wax bite impression is then employed to register the upper and lower teeth castings while the castings are trimmed or surfaced on their posterior faces or while an articulator is attached to the castings. This procedure entails a large amount of time, labor, cost, sometimes patient discomfort, and has many opportunities for inaccuracy of registration, all of which are greatly reduced by the system disclosed herein.